Estrogens and progestogens

Transcription

1 Estrogens and progestogens Estradiol and Progesterone hormones produced by the gonads are necessary for: conception embryonic maturation development of primary and secondary sexual characteristics at puberty. The gonadal hormones are used therapeutically in replacement therapy for contraception management of menopausal symptoms. several antagonists are effective in cancer chemotherapy. Estrogens Estradiol, (17-β-estradiol) Is the most potent estrogen produced and secreted by the ovary. It is the principle estrogen in the premenopausal woman. Estrone is a metabolite of estradiol that has approximately one-third the estrogenic potency of estradiol. Estrone is the primary circulating estrogen after menopause. Estriol, is another metabolite of estradiol, it is significantly less potent than estradiol. It is present in significant amounts during pregnancy because it is the principal estrogen produced by the placenta. 1

2 Plant-derived conjugated estrogen products are also available, which are presents in fruits and vegetable and nuts such as; Apricots, Dates, Peaches, Strawberries, Green Beans, Pistachios, Walnuts, Peanuts. Synthetic estrogens, such as ethinyl estradiol, undergo less first-pass metabolism than naturally occurring steroids and, thus, are effective when administered orally at lower doses. Selective estrogen-receptor modulators Nonsteroidal compounds that bind to estrogen receptors and exert either estrogenic or antiestrogenic effects on target tissues are called selective estrogen-receptor modulators. These include tamoxifen and raloxifene. Mechanism of action of estrogens After dissociation from their binding sites on sex hormone-binding globulin or albumin in the plasma, steroid hormone diffuse across the cell membrane and bind with high affinity to specific nuclear-receptor proteins. The activated steroid-receptor complex results in the synthesis of specific proteins that mediate a number of physiologic functions. Two estrogen-receptor subtypes, α and β, mediate the effects of the hormone. These receptor isoforms vary in structure, chromosomal location, and tissue distribution. The steroid hormones may elicit the synthesis of different RNA species in diverse target tissues and, therefore, are both receptor and tissue specific. 2

3 Therapeutic uses of estrogens contraception Postmenopausal hormone therapy [estrogen-progestogen therapy (EPT)]. Replacement therapy in premenopausal patients who are deficient in this hormone. Such a deficiency can be due to inadequate functioning of the ovaries (hypogonadism), premature menopause surgical menopause. 1. Postmenopausal hormone therapy: The primary indication for estrogen therapy is menopausal symptoms vasomotor instability (for example, hot flash) For women who have undergone a hysterectomy (uterus has been surgically removed). However for women who have an intact uterus, a progestin is always included with the estrogen therapy, because the combination reduces the risk of endometrial carcinoma associated with unopposed estrogen. 3

4 Note: The amount of estrogen used in replacement therapy is substantially less than the doses used in oral contraception. Thus, the adverse effects of estrogen replacement therapy are usually less pronounced than those seen in women taking estrogen for contraceptive purposes. 2. Contraception: The combination of an estrogen and progestogen provides effective contraception via different dosage form. 3. Other uses: Estrogen in combination with a progestogen, Is used to stimulate development of secondary sex characteristics in young women with primary hypogonadism. Continued treatment is required after growth is completed. is used for women who have premature menopause. premature ovarian failure. Pharmacokinetics Naturally occurring estrogens: They are readily absorbed through the gastrointestinal tract, skin, and mucous membranes. Taken orally, estradiol is rapidly metabolized (and partially inactivated) by the microsomal enzymes of the liver. Micronized estradiol is available and has better bioavailability. 4

5 Synthetic estrogen analogs These compounds, such as ethinyl estradiol and mestranol, are well absorbed after oral administration or through the skin or mucous membranes. Mestranol is quickly demethylated to ethinyl estradiol, which is metabolized more slowly than the naturally occurring estrogens by the liver and peripheral tissues. Being fat soluble, they are stored in adipose tissue, from which they are slowly released. Therefore, the synthetic estrogen analogs have a prolonged action and a higher potency compared to those of natural estrogens. Metabolism: Estrogens are transported in the blood while bound to serum albumin or sex hormone-binding globulin. Bioavailability of estrogen taken orally is low due to first-pass metabolism in the liver. To reduce first-pass metabolism, the drugs may be administered by other routes for example by transdermal patch, topical gel or injection. Estrogens are hydroxylated in the liver to derivatives that are subsequently glucuronidated or sulfated. The parent drugs and their metabolites undergo excretion into the bile and are then reabsorbed through the enterohepatic circulation. Inactive products are excreted in the urine. Adverse effects Nausea and breast tenderness are among the most common adverse effects of estrogen therapy. 5

6 In addition, the risk of thromboembolic events, myocardial infarction, and breast and endometrial cancer is increased with use of estrogen therapy. [Note: The increased risk of endometrial cancer can be offset by including a progestogen along with the estrogen therapy.] Selective Estrogen-Receptor Modulators (SERMs) SERMs are a class of estrogen-related compounds that display selective agonism or antagonism for estrogen receptors depending on the tissue type. This category includes tamoxifen, toremifene, raloxifene and clomiphene. A. Tamoxifen It is estrogen antagonist. Uses: Treatment of metastatic breast cancer in postmenopausal women. Adjuvant therapy following mastectomy or radiation Reducing the risk of breast cancer in high-risk patients. Adverse effects: Hot flashes Nausea endometrial hyperplasia and malignancies Because Tamoxifen is metabolized by various CYP450 isoenzymes, tamoxifen is subject to many drug interactions. 6

7 B. Raloxifene Raloxifene is a second-generation SERM. Raloxifene has been shown to reduce the incidence of invasive breast cancer in postmenopausal women. Used in treatment of osteoporosis (because of its ability to decrease bone resorption and overall bone turnover. increases Bone density, and decreases vertebral fractures) It has no effect on the endometrium and, therefore, may not predispose to uterine cancer. Raloxifene lowers total cholesterol and low-density lipoprotein (LDL) in the serum. Adverse effects: Hot flashes and leg cramps Increased risk of deep-vein thrombosis, pulmonary embolism, and retinalvein thrombosis. Coadministration with cholestyramine can reduce the absorption of raloxifene by 60 percent; therefore, these drugs should not be taken together. 7

8 C. Toremifene Toremifene is a SERM with properties and side effects similar to those of tamoxifen. Uses: postmenopausal women with metastatic breast cancer. D. Clomiphene By acting as a partial estrogen agonist and interfering with the negative feedback of estrogens on the hypothalamus, clomiphene increases the secretion of gonadotropin-releasing hormone and gonadotropins, leading to a stimulation of ovulation. The drug has been used successfully to treat infertility associated with anovulatory cycles, but it is not effective in women with ovulatory dysfunction due to pituitary or ovarian failure. Adverse effects: headache, nausea, vasomotor flushes, visual disturbances, and ovarian enlargement. Use of clomiphene increases the risk of multiple births (twins or triplets). Progestogens: Progesterone, the natural progestogens, is produced in response to luteinizing hormone (LH) Secreted by the corpus luteum, primarily during the second half of the menstrual cycle by the placenta by males (secreted by the testes). It is also synthesized by the adrenal cortex in both genders. 8

9 Mechanism of action Progestogens exert their mechanism of action in a manner analogous to that of the other steroid hormones. In females, progesterone promotes the development of a secretory endometrium that can accommodate implantation of a newly forming embryo. The high levels of progesterone that are released during the second half of the menstrual cycle (the luteal phase) inhibit the production of gonadotropin and, therefore, prevent further ovulation. If conception takes place, progesterone continues to be secreted, maintaining the endometrium in a favorable state for the continuation of the pregnancy and reducing uterine contractions. If conception does not take place, the release of progesterone from the corpus luteum ceases abruptly. This decline stimulates the onset of menstruation. Progestins also cause: 1) An increase in hepatic glycogen. 2) A decrease in Na+ reabsorption in the kidney due to competition with aldosterone at the mineralocorticoid receptor 3) An increase in body temperature through an unknown mechanism 4) A decrease in some plasma amino acids 5) An increase in excretion of urinary nitrogen. 9

10 Therapeutic uses of progestins to rectify a hormonal deficiency Contraception, in which they are generally used with estrogens, either in combination or in a sequential manner. Synthetic progestins used in contraception are more stable to first-pass metabolism, allowing lower doses when administered orally. These agents include norethindrone norethindrone acetate norgestrel levonorgestrel desogestrel Norgestimate drospirenone Most synthetic progestins used in oral contraceptives (for example, norethindrone, norethindrone acetate, norgestrel, levonorgestrel) are derived from 19- nortestosterone and possess some androgenic activity because of their structural similarity to testosterone. Other clinical uses of the progestins are in the control of dysfunctional uterine bleeding treatment of dysmenorrhea management of endometriosis. 10

11 Medroxyprogesterone acetate is injected intramuscularly or subcutaneously and has duration of action of 3 months. The other progestins last from 1 to 3 days. Adverse effects Headache, depression, weight gain. progestins, such as the 19-nortestosterone derivatives, have androgenic activity and can increase the ratio of LDL to HDL cholesterol and cause acne and hirsutism. Less androgenic progestins, such as norgestimate and drospirenone, may be preferred in women with acne. Injectable medroxyprogesterone acetate has been associated with an increased risk of osteoporosis, which has led to recommendations for limiting the duration of use. Antiprogestin It s a progesterone antagonist with partial agonist activity. [Note: Mifepristone also has potent antiglucocorticoid activity.] Administration of this drug to females in early pregnancy results in most cases (up to 94 percent) in abortion of the fetus due to the interference with progesterone and the decline in human chorionic gonadotropin. Adverse effects: uterine bleeding Possibility of an incomplete abortion. However, administration of misoprostol after a single oral dose of mifepristone effectively terminates gestation. Mifepristone is being investigated as an oral contraceptive and an emergency contraceptive agent. 11